In this document, dynamic range control refers to a class of dynamic range processors such as a limiter, a compressor, and/or processors. When an input signal is below a threshold, the limiter, compressor, and/or processors produce an output signal having a linear relationship to the input signal. When the input signal exceeds a threshold, the limiter, compressor, and/or processors apply a time varying gain to the input signal to achieve a dynamic range goal for the output signal.
There are many instances when it can be desirable to reduce a dynamic range of an audio signal, such as by dynamic range compression, limiting, or a combination of the two, often referred to as compression/limiting.
Such dynamic range reduction can be useful for digital audio systems. Most digital system have a fixed maximum peak volume, denoted by 100%. As an example, if the volume of a musical piece is reduced overall so that a particularly loud portion does not clip (e.g., exceed 100% of the maximum volume level of the digital audio system), then softer portions of the musical piece may be inaudible or difficult to hear. Dynamically reducing the volume of just the loud portion, but not the softer portions, can allow the overall volume of the musical piece to be raised to a more reasonable level, which can improve listening in a noisy environment, such as an automobile.
Such dynamic range reduction can also be useful for analog audio systems. For example, phonograph records are subject to mechanical constraints that dictate how loud the recorded levels can be, where a portion that is too loud can cause the phonograph needle to skip. Reducing the overall volume of the material on the record can be unsatisfactory, because the softer material can get lost in a surface noise floor from the record. Dynamically reducing the volume of just the loud portions of the material, but not the softer portions, can allow the overall volume of the musical piece to be raised to a more reasonable level so that it is well above the noise floor of the record.
Dynamic range reduction is straightforward for a single-channel audio signal, such as a live feed from a microphone or instrument, or a monaural (mono) recording from the pre-stereo era. Compressor/limiters are readily available for single-channel inputs and single-channel outputs.
However, dynamic range reduction is significantly more complicated for a multi-channel audio signal, such as a stereo audio signal, especially when coupled with spatial enhancement processing, such as widening the soundstage of the stereo audio signal. In some examples, the dynamic range reduction can introduce volume-related and/or panning-related artifacts into the multi-channel audio signal.
Accordingly, there exists a need for audio processing that can apply dynamic range reduction for a multi-channel audio signal, without introducing volume-related and/or panning-related artifacts into the multi-channel audio signal.
Corresponding reference characters indicate corresponding parts throughout the several views. Elements in the drawings are not necessarily drawn to scale. The configurations shown in the drawings are merely examples, and should not be construed as limiting the scope in any manner.